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Geotechnical properties of ash deposits near Hilo, Hawaii

Open-File Report 82-279
By: , , , and 
https://doi.org/10.3133/ofr82279

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Abstract

Two holes were hand augered and sampled in ash deposits near Hilo, Hawaii. Color, water content and sensitivity of the ash were measured in the field. The ash alternated between reddish brown and dark reddish brown in color and had water contents as high as 392%. A downhole vane shear device measured sensitivities as high as 6.9. A series of laboratory tests including grain size distribution, Atterberg limits, X-ray diffraction analysis, total carbon determination, vane shear, direct shear and triaxial tests were performed to determine the composition and geotechnical properties of the ash. The ash is very fine grained, highly plastic and composed mostly of gibbsite and amorphous material presumably allophane. The ash has a high angle of internal friction ranging from 40-43? and is classified as medium to very sensitive. A series of different ash layers was distinguished on the basis of plasticity and other geotechnical properties. Sensitivity may be due to a metastable fabric, cementation, leaching, high organic content, and thixotropy. The sensitivity of the volcanic ash deposits near Hilo is consistent with documented slope instability during earthquakes in Hawaii. The high angles of internal friction and cementation permit very steep slopes under static conditions. However, because of high sensitivity of the ash, these slopes are particularly susceptible to seismically-induced landsliding.
Publication type Report
Publication Subtype USGS Numbered Series
Title Geotechnical properties of ash deposits near Hilo, Hawaii
Series title Open-File Report
Series number 82-279
DOI 10.3133/ofr82279
Edition -
Year Published 1982
Language ENGLISH
Publisher U.S. Geological Survey,
Description 20 p., ill., maps ;28 cm.
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